Separation of nitriles



Patented Nov. 8, 1949 SEPARATION oF' NITRILES Richard B. Bishop,Haddonfield,-N. J assignor to Socony-Vacuum Oil Company,'.lncorporated,a

corporation of New York No Drawing. Application February 6, 1948, SerialNo. 6,799

This invention relates to the separation of nitriles from mixturescontaining them, and particularly to the separation of aromaticpolynitriles from mixtures which also contain aromatic mononitriles andhydrocarbons.

In accordance with the following patent applications, aromaticmononitriles and aromatic polynitriles can be prepared by reactingaromatic hydrocarbons with ammonia, at elevated temperatures and in thepresence of a catalyst selected from the group consisting of molybdenumoxide, tungsten oxide, and vanadium oxide: Serial No. 641,640, filedJanuary 16, 1946, nowPatent No. 2,450,632, and Serial No. 643,742, filedJanuary 26, 1946, now abandoned by Caldwell and Chapman; Serial No.649,118, filed February 20, 1946, now Patent No. 2,450,639, and SerialNo.- 653,435, filed March 9, 1946, now Patent No. 2,450,640, by Dentonand Bishop.

In preparing nitriles in accordance with the teachings of theaforementioned applications, it has been found desirable to use amixture of hydrocarbons such as, for example, an aromatic solventobtained from catalytic cracking, which is a mixture of hydrocarbonsabout 60% to 70% of which are aromatic, and which has a boiling range offrom about 280 to 370 F., a specific gravity of about 0.8443 and a mixedaniline point of about 79 F.

The products resulting from carrying out the processes of the aboveapplications consist of a mixture of various hydrocarbons and variousaromatic nitriles, and when part of the aromatics used in the chargehave more than one side chain, aromatic polynitriles are formed as Wellas aromatic mononitriles.

While most of the aromatic mononitriles and hydrocarbons may beseparated from'the aromatic polynitriles by distillation, if thetemperature of the distillation is carried too high, sub limation of thearomatic polynitriles interferes with the separation, andpolymerization, charring and other deterioration of the products islikely to result. As a consequence, it is preferred to remove asubstantial portion of the hydrocarbons and aromatic mononitriles bydistillation, leaving a residue of black, tarry, high-boiling compounds,which includes the aromatic polynitriles and certain high-boilinghydrocarbons and a minor amount of aromatic mononitriles.

Experience has shown that the separation of aromatic nitriles fromhydrocarbons, and the separation of aromatic polynitriles from aromaticmononitriles, is not always easy of accomplishment. For example, Ralstonand Pool in United 2 Claims. (Cl. 260465) mononitriles. Furthermore, thehydrocarbons in I States Letters Patent 2,133,007, explain atconsiderable length the difficulties encountered in the separation ofaliphatic nitriles from admixtures thereof with hydrocarbons. Thedifficulties encountered in such separations, however, are not nearly sosevere as the difficulties encountered in attempting to separatearomatic polynitriles from the black, tarry, high-boiling residuedescribed hereinbefore, which contains not only aromatic polynitrilesand hydrocarbons, but also aromatic this black, tarry residue arehigh-boiling hydrocarbons that are far more difficult to separate fromthe aromatic polynitriles than would be the ;simple, low-boilinghydrocarbons of the Ralston lem that is different from the problems ofordinary solvent extraction. Far more difficult is the i problem ofextracting aromatic polynitriles from the black, tarry, high-boilingresidue described above. The water-alcohol mixtures of Ralston r andPool are completely inefiective for this purfound that thishigh-boiling, black, tarry material maybe extracted with absolute ethylalcohol or above) and the aromatic polynitriles contained therein thusisolated. This solvent dissolves almost the entire product While hot buton cooling throws out as a precipitate practically all of the aromaticpolynitriles, while maintaining in solution the hydrocarbons andaromatic mononitriles. The extraction is preferably accomplished byheating and stirring the tarry mixture with the absolute alcohol,filtering and, thereafter, reducing the temperature sufficiently tocause crystallization of the dissolved aromatic polynitriles. Thearomatic polynitriles so recovered can be redissolved andrecrystallized, or sublimed, to further purify them.

A small amount of aromatic mononitriles can usually be recovered fromthe solvent after the aromatic polynitriles have been recovered, bydistilling ofi the solvent and iractionally distilling the liquidproduct that is left behind. Once the aromatic mononitriles have beendistilled from this liquid product, the remainder contains practicallyno nitrogen.

A further understanding of the details and advantages of this inventionmay be had by consideration of the following specific example,

Example p-Xylene and ammonia were passed over a molybdenum oxidecatalyst at about 1000 F. at 90 lbs/sq. in. gauge pressure in amolecular ratio of 2:1. The product was distilled to recover theunreactedip-xylene and mostof. the aromatic mononitriles formed. Theresidue-was a. mixture of black, tarry, high-boiling compounds. Thisresidue (610 g.) was treated with 3 liters of alco+ hol (95%) by heatingand stirring andthenvfiltering. The filtrate was chilled to a.temperature of about C. whereupon 185. g; of arbrownishh powderseparated. This powder wasagain dissolved in alcohol (95%), filtered,and again crystallized by chilling to about 0 C. Another portion waspurified by sublimation. Both portions had a melting point of 226 C.,which corresponds to terephthalic nitrile, (dinitrile L-di'cyan'obenzene), which, according to the literature, has ameltingpoint'of- 226C; The alcoholused: for the separation was: distilled leaving: a.-quantity: ofa yellow liquid oil. This oil was vacuum distilled at 4' mm;of mar-- bury pressure and a minorrquantity of aromatic mononit'rileswasobtained therefrom; The remainder containedn'practicall'y no. nitrogen.

Whiie'this invention has been explained as appliedto a particulartype-of mixture of' aromatic Any, amount vsuflicient to dissolve-allrorsubstan tially all ofthe aromatic polynitriles atthe tern-,-

perature applied, will be satisfactory. Large ex-- cesses overthis-amount will obviously Ifv sufiicient quantities of absolute alcoholare used ancl,;the treatment continued long enough, the aromaticpolynitriles can be dissolved With.- out any heating; However-, itis'preferred'to heat the alcohol sufiiciently to increaseits solventpowbe. impracerinsofar as is practical, under-the: conditions;

of operation. Thus when operating, in open vessels the alcohol cannot beheated above its boil-- ing point. However, when the operation isacrather than by cooling if so desired, but this is a less preferredmodification. Whatis claimed is:

1; A method of'separating aromatic polynitriles from a mixture ofaromatic polynitriles, aromatic mononi'tri-l-esand aromatichydrocarbons, which comprises treating said mixture with hot ethylalcohol containing not more than 5 per cent water to dissolve thearomatic polynitriles to form an alcohol extra-ct, separating saidalcohol extract,

lowering the temperature of said alcohol extract suflicientlyto'precipitate said aromatic polynitrl-les' in preference to thearomaticmononi-trlles' and'aromatic hydrocarbons; and separat-- ing saidaromatic pol-ynitriles from said alcohol extract.

2. "'A- method of separating dicyano benzene from a mixture ofdicyanoben'zene, xylene and tol-uonitrile, which comprisestreating saidmixture with-hot ethyl alcohol containing not more than Ei-per centwaterto dissolve the dicyano benzene to form an alcohol extract;separating said alcohol extract, lowering the temperature of saidalcohol extract sufficiently to precipitate said di-cya-no benzene inpreferencetothe toluonitrile and xylene, and separating dicyano benzenefromsaid'alcohol extract;

" RICHARD B. BISHOP.

REFERENCES CITED The following references are of record in the,

file of this. patent:

STATES PATENTS Number Name Date 2,133,007 Ralston et a1. Oct. 11,19382,' 1'74',568 Davies vet a1. Oct. 3, 193.9 2,305,529. Hester et a1. Dec.15, 1942 OTHER REFERENCES Gattermann, ""Org. Chemistry (Macimillan,1896), p 1-15;

